1. Technical Field
Embodiments of the present invention relate to cryosurgical equipment, and, more particularly, to cryoprobes or cryocatheters that feature a flow diverter that directs the incoming flow of cryogen against the inner wall of the external shaft thereof.
2. Description of Background Art
This description of background art is intended to provide the basic context of this patent application.
Cryoprobes that “boil” a liquid cryogen, when this liquid cryogen is supplied from an external source into the cryoprobe, are known for performing cryosurgical procedures. Generally, a cryogen is delivered into a cryoprobe in the form of a two-phase fluid, since a certain percentage of the liquid cryogen evaporates inevitably before entry to the cryoprobe as a result of imperfect thermal insulation of the delivery hose. This two-phase condition cannot easily be improved by separating the liquid and gaseous phases completely in the internal cavity of the cryotip (the distal section of the cryoprobe) without the implementation of special structures. In addition, in particular when nitrogen is used as a cryogen, the liquid nitrogen interacts with the solid, warmer surface by creating nitrogen gas cushion, known as Liedenfrost effect. This effect considerably reduces the ability to absorb heat from the warmer surface. Without addressing the problems caused by this cushion, it is impossible to take advantage of the boiling of the liquid fraction of the cryogen for effective freezing of a treated tissue. A more desirable solution would force the “boiling” of the liquid phase to take place as close as possible to the warmer surface.
Attempted solutions to these problems associated with using nitrogen as the cryogen are known; all suffer from significant drawbacks, however, due to the nature of boiling nitrogen fluid flow.
Joule-Thomson probes inherently operate such that the cryogen is delivered to an expansion chamber at the end of the tip, where it expands and cools. After cooling, the expanded and cooled cryogen then enters a return passage where it cools the external surface. When cooled by evaporation, the volume of the returning cryogen is considerably larger than the amount of cryogen initially supplied to the cryoprobe. Such an expanded volume of the return cryogen poses considerable difficulty for removal from the cryoprobe, due to the relatively small confines of the available exit(s) for exhausting the expanded cryogen.